1. Field of the Invention
The present invention relates to a dielectric filter used in an automobile telephone and the like.
2. Description of the Related Art
Hitherto, a conventional dielectric filter typically has a construction shown in FIG. 2.
In FIG. 2 the numeral 1 represents dielectric coaxial resonators of .lambda. /4 type which are arranged in a row on a substrate 2. FIG. 3 shows an electric circuit diagram which corresponds to the filter of FIG. 2.
These dielectric coaxial resonators 1 are electrically connected in parallel through a capacitance (represented by the numeral 3 in FIG. 3) formed on a substrate 2. Because of this arrangement, the filter has for example a sending band illustrated by hatching in FIG. 4.
The symbol A in FIG. 4 is a pole to ensure an increased amount of attenuation at a high-frequency region. This attenuation is necessary to clearly separate the sending band from a receiving band at the high frequency region.
The pole A is formed by an inductance 4 which is electrically connected in parallel to the capacitance 3 as illustrated in FIG. 3. The inductance 4 is constituted by a pattern formed on the substrate 5 shown in FIG. 2.
In FIG. 3, the numerals 6 and 7 are respectively an input terminal and an output terminal.
However, a conventional filter in which a pole A is obtained by an inductance 4 formed on a substrate 5 has a drawback in that, as readily understandable from FIG. 2, the overall height of the filter is increased by the additional height due to the substrate 5.
In view of the recent circumstances in which an automobile telephone has become more and more compact, the above-mentioned drawback of increased overall height is really an important problem.